This invention relates generally to devices useful for illuminating display units, and specifically to illuminated display units which can be retrofitted into existing incandescent light bulb sockets.
Most public buildings now require perpetually lighted exit signs to direct people out of the buildings in case of an emergency. Usually such exit signs are powered by the normal building electrical power supply.
Problems arise, however, when the nature of the emergency causes the building power supply to go out. This shuts down the exit signs, defeating their purpose.
In an attempt to get around this problem, many building codes are now requiring that the exit signs have an independent, back-up power supply. The theory is that, if the main power supply goes out, the back-up power supply will continue to maintain the signs in a lighted state. However, most prior back-up power supply systems utilize a remote source of power, such as a generator. Because such power back-up source is remote, long runs of electrical wiring must often be used to connect the back-up remote source to the individual exit signs. Such wiring can be damaged during a fire or other catastrophic disaster.
Some installations use battery packs as the backup system for emergency signs. Each sign has its own battery pack located somewhere in the vicinity of the illuminating units. However, this is not entirely satisfactory either. Such battery packs still require some amount of external wiring to electrically connect the battery pack to the signs. Such wiring is damageable and requires labor and time for installation. Moreover, battery packs must generally be monitored closely to make sure the batteries never run down. Also, battery packs are bulky and difficult to hide in a way where they can be easily maintained and where the batteries can be periodically replaced.
These problems with prior art back-up devices become even more acute where an existing sign must be upgraded to include an independent back-up power supply. Utilizing a remote source of electrical power is even less satisfactory than in new installations since, in addition to the disadvantages mentioned above, installation requires extensive rewiring of the entire building. Utilizing individual battery packs is also less satisfactory because hiding the bulky, unsightly battery packs generally requires substantial remodeling efforts.
Accordingly, there is a pressing need for a system which will provide emergency back-up power to exit signs and other emergency signs which does not rely on a remote power source or extra wiring. Such a system should not require the "hiding" of a battery pack unit. Such a system should be able to utilize small and manageable battery packs. Such a system should not require the continued monitoring and frequent replacement of the batteries. Such a system should be easy to maintain. There is also a need for such a system which is easily and inexpensively "retrofittable" into existing exit signs.